From: Mel Gorman <mgorman@techsingularity.net>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Vlastimil Babka <vbabka@suse.cz>, Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 20/22] mm, page_alloc: Check multiple page fields with a single branch
Date: Mon, 11 Apr 2016 09:13:43 +0100 [thread overview]
Message-ID: <1460362424-26369-21-git-send-email-mgorman@techsingularity.net> (raw)
In-Reply-To: <1460362424-26369-1-git-send-email-mgorman@techsingularity.net>
Every page allocated or freed is checked for sanity to avoid corruptions
that are difficult to detect later. A bad page could be due to a number of
fields. Instead of using multiple branches, this patch combines multiple
fields into a single branch. A detailed check is only necessary if that
check fails.
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
mm/page_alloc.c | 55 +++++++++++++++++++++++++++++++++++++++++++------------
1 file changed, 43 insertions(+), 12 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8f53cb3853fc..59d7c627b29d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -784,10 +784,42 @@ static inline void __free_one_page(struct page *page,
zone->free_area[order].nr_free++;
}
+/*
+ * A bad page could be due to a number of fields. Instead of multiple branches,
+ * try and check multiple fields with one check. The caller must do a detailed
+ * check if necessary.
+ */
+static inline bool page_expected_state(struct page *page,
+ unsigned long check_flags)
+{
+ if (unlikely(atomic_read(&page->_mapcount) != -1))
+ return false;
+
+ if (unlikely((unsigned long)page->mapping |
+ page_ref_count(page) |
+#ifdef CONFIG_MEMCG
+ (unsigned long)page->mem_cgroup |
+#endif
+ (page->flags & check_flags)))
+ return false;
+
+ return true;
+}
+
static inline int free_pages_check(struct page *page)
{
- const char *bad_reason = NULL;
- unsigned long bad_flags = 0;
+ const char *bad_reason;
+ unsigned long bad_flags;
+
+ if (page_expected_state(page, PAGE_FLAGS_CHECK_AT_FREE)) {
+ page_cpupid_reset_last(page);
+ page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
+ return 0;
+ }
+
+ /* Something has gone sideways, find it */
+ bad_reason = NULL;
+ bad_flags = 0;
if (unlikely(atomic_read(&page->_mapcount) != -1))
bad_reason = "nonzero mapcount";
@@ -803,14 +835,8 @@ static inline int free_pages_check(struct page *page)
if (unlikely(page->mem_cgroup))
bad_reason = "page still charged to cgroup";
#endif
- if (unlikely(bad_reason)) {
- bad_page(page, bad_reason, bad_flags);
- return 1;
- }
- page_cpupid_reset_last(page);
- if (page->flags & PAGE_FLAGS_CHECK_AT_PREP)
- page->flags &= ~PAGE_FLAGS_CHECK_AT_PREP;
- return 0;
+ bad_page(page, bad_reason, bad_flags);
+ return 1;
}
/*
@@ -1491,9 +1517,14 @@ static inline void expand(struct zone *zone, struct page *page,
*/
static inline int check_new_page(struct page *page)
{
- const char *bad_reason = NULL;
- unsigned long bad_flags = 0;
+ const char *bad_reason;
+ unsigned long bad_flags;
+
+ if (page_expected_state(page, PAGE_FLAGS_CHECK_AT_PREP|__PG_HWPOISON))
+ return 0;
+ bad_reason = NULL;
+ bad_flags = 0;
if (unlikely(atomic_read(&page->_mapcount) != -1))
bad_reason = "nonzero mapcount";
if (unlikely(page->mapping != NULL))
--
2.6.4
--
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next prev parent reply other threads:[~2016-04-11 8:16 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-11 8:13 [PATCH 00/21] Optimise page alloc/free fast paths Mel Gorman
2016-04-11 8:13 ` [PATCH 01/22] mm, page_alloc: Only check PageCompound for high-order pages Mel Gorman
2016-04-11 8:13 ` [PATCH 02/22] mm, page_alloc: Use new PageAnonHead helper in the free page fast path Mel Gorman
2016-04-11 8:13 ` [PATCH 03/22] mm, page_alloc: Reduce branches in zone_statistics Mel Gorman
2016-04-11 8:13 ` [PATCH 04/22] mm, page_alloc: Inline zone_statistics Mel Gorman
2016-04-11 8:13 ` [PATCH 05/22] mm, page_alloc: Inline the fast path of the zonelist iterator Mel Gorman
2016-04-11 8:13 ` [PATCH 06/22] mm, page_alloc: Use __dec_zone_state for order-0 page allocation Mel Gorman
2016-04-11 8:13 ` [PATCH 07/22] mm, page_alloc: Avoid unnecessary zone lookups during pageblock operations Mel Gorman
2016-04-11 8:13 ` [PATCH 08/22] mm, page_alloc: Convert alloc_flags to unsigned Mel Gorman
2016-04-11 8:13 ` [PATCH 09/22] mm, page_alloc: Convert nr_fair_skipped to bool Mel Gorman
2016-04-11 8:13 ` [PATCH 10/22] mm, page_alloc: Remove unnecessary local variable in get_page_from_freelist Mel Gorman
2016-04-11 8:13 ` [PATCH 11/22] mm, page_alloc: Remove unnecessary initialisation " Mel Gorman
2016-04-11 8:13 ` [PATCH 12/22] mm, page_alloc: Remove unnecessary initialisation from __alloc_pages_nodemask() Mel Gorman
2016-04-11 8:13 ` [PATCH 13/22] mm, page_alloc: Remove redundant check for empty zonelist Mel Gorman
2016-04-11 8:13 ` [PATCH 14/22] mm, page_alloc: Simplify last cpupid reset Mel Gorman
2016-04-11 8:13 ` [PATCH 15/22] mm, page_alloc: Move might_sleep_if check to the allocator slowpath Mel Gorman
2016-04-11 8:13 ` [PATCH 16/22] mm, page_alloc: Move __GFP_HARDWALL modifications out of the fastpath Mel Gorman
2016-04-11 8:13 ` [PATCH 17/22] mm, page_alloc: Reduce cost of fair zone allocation policy retry Mel Gorman
2016-04-11 8:13 ` [PATCH 18/22] mm, page_alloc: Shortcut watermark checks for order-0 pages Mel Gorman
2016-04-11 8:13 ` [PATCH 19/22] mm, page_alloc: Avoid looking up the first zone in a zonelist twice Mel Gorman
2016-04-11 8:13 ` Mel Gorman [this message]
2016-04-11 8:13 ` [PATCH 21/22] cpuset: use static key better and convert to new API Mel Gorman
2016-04-11 8:18 ` [PATCH 00/21] Optimise page alloc/free fast paths Mel Gorman
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